[xwiki-users] Subpage permission

Hi, I've started working with XWiki for a short time and I'm facing a probem with the rights management. I configured XWiki so every registered users have read permission as default. Then I created some private spaces with read access for a specific group of users. Let's say group A has read permission on space A. Other groups don't have access to this space A. So it is fine. But I need sometimes to allow some specific groups or users to access some specific pages in this space. For example, group B should have read access on page 1 of space A. I modified the access rights of the page accordingly. The problem is: it doesn't work when the page is a subpage. It is working fine if the page is at the root of the space. Is it a normal behaviour? What shall I do to make this work? Thanks. Yvan Arnaud